One of the problem areas in the packaging industry concerns the overwrap packaging of goods, particularly the unitization of pallet loads. Ideally, an overwrap material should have high strength, be resistant to tear and puncture, and exhibit single-sided cling properties. In particular, single-sided cling properties are required in order to prevent individual pallets from clinging to each other and being torn or destroyed when being separated from each other.
Development of single-sided cling has, generally, been directed toward surface modifying one side of an A/B film. For example, U.S. Pat. No. 4,820,589 discloses an A/B film structure, wherein the A layer has a comparatively high cling force to layer B and layer B has substantially less cling force to a layer of itself. The B layer contains nylon. Further, single and two-layer film structures are further disclosed in U.S. Pat. Nos. 4,518,654 and 4,833,017, herein incorporated by reference. In U.S. Pat. No. 4,518,654, the "non-cling" B layer is a polyolefin with an anti-cling additive such as crystalline or amorphous silica, sodium aluminum silicate, diatomaceous earth, and talc. It is not possible to obtain a zero cling force for the B layer, however, since the additive must be present in minimal quantities in order to prevent tearing or fracturing of the film. Further, the coefficient of friction of such films is greater than 2.0 which indicates an unfavorable slideability property of the B layer. Also further, the minimum stretch capability of such films is approximately 50%. Thus, such films neither exhibit a truly cling-free layer or the maximum tensile strength and minimum stretch capability which is commercially demanded.
In order to prevent the tearing or loosening of the wrapping on stacked overwrapped pallet loads, it would be highly desirable to have a tough film exhibiting high tensile strength and greater elongation with good cling properties on one side to engage the contained load and little or no cling properties on the other side to avoid clinging to neighboring stacked, wrapped loads.